Nirmal and Sushma are standing in a queue of people facing north. Nirmal is at the 20th position from the extreme left end, and Sushma is at the 10th position from the extreme right end. The positions of Nirmal and Sushma are interchanged due to some criteria based on age. If the new position of Nirmal is 30th from the extreme left end, then what is the new position of Sushma from the extreme right end?
A25th
B30th
C18th
D20th